Generally a planetary gear reduction system includes an input shaft connected to a sun gear and an output shaft connected to a planetary carrier. Torque is typically applied to the input shaft in at least one direction of rotation which results in an increased torque in the same direction at the output shaft. If the planetary gear system is used to deflect an elastic system, when the torque is removed from the input shaft, there is strain energy in the system. The strain energy applies a torque on the output shaft opposite of the torque that was applied to the input shaft. The strain energy results in the system back-driving, such that the torque that was applied to the output shaft is at least partially released. Attempts have been made to incorporate a “self-locking” feature to ensure that the force applied to the planetary gear reduction system so that torque is maintained after the motor applied current is turned off. The self-locking function is typically incorporated in the system by using an element which cannot be back-driven, such as a worm type reduction gear or a short pitch drive screw. However, these elements, which cannot be back-driven, incorporate friction levels which are incompatible with high efficiency so that either speed is sacrificed or a larger motor is used to achieve a desired result.
Examples of brake systems using one-way clutches are disclosed in U.S. Pat. Nos. 7,648,014 and 6,938,736 which are expressly incorporated herein by reference for all purposes. It would be attractive to have a planetary gear assembly that is able to prevent back-driving and a planetary gear assembly which is able to retain the torque applied to the output shaft without having to continuously apply torque to the input shaft. What is needed is a planetary gear assembly compatible with a braking system in which the system allows use of high efficiency mechanisms for speed reduction and rotary to linear conversion stages. What is needed is a system which can reduce the size and cost of components.